stumblematic uses a script which was written for stumblebot.net. The writer of the script sold stumblebot.net for
$6000.
After the sale the website disppeared. Maybe stumbleupon bought it and killed it off.
You can try to contact the seller via sitepoint and see if he will pass it on but I don't think it will come cheap.
I am writing a similar script for linkarena.com would that be of interest??